1. Field of the Invention
The present invention relates to a method and a device for connecting networks each of which can be used for communications between all kinds of multi-media terminals, and in particular a method and a device for connecting networks each of which is beneficial to the kind of machines for calling and connecting terminals, which exist among different multi-media communication networks given different address spaces.
2. Description of Related Art
Recently, there is an explosion of business activities taking place on the Internet. As vast numbers of corporate networks are now connected to the Internet, IP address depletion and scaling are becoming the most compelling problems. So the solutions to these problems are being developed.
There has been published some technical documents about above-mentioned solutions to be disclosed hereinafter, which are RFC1631 The Ip Network Address Translator (NAT),RFC2319 Load Sharing Using IP Network Address Translation (LSNAT),ITU-T H323 Packet Based Multi-media Communication Systems, and RFC2543 Session Initiation Protocol (SIP).
The most adequate short-term solution to solve the IP address problems mentioned above is to reuse addresses in the different domains (cf. RFC1631). Thus each domain is given a different address space which is different from the other domains. However, there should be the case that a terminal in a domain given an address space would like to communicate with another terminal in another domain given another address space.
By the way, in the conventional IP network, such devices as NAT (Network Address Translator) or NAPT (Network Address Port Translation) have been used for the IP packets transferring between different address spaces.
NAT and NAPT devices are located at the edge of the address space, and change addresses, either statically or dynamically, for the IP packets transferring to the different address space. NAT device translates one internally-used IP address to one globally unique IP address. In contrast to this, NAPT device multiplexes transport layer identifiers of internal hosts into the transport identifiers of the single assigned external address.
Hereinafter, I would like to explain the address transfer method of NAT device by means of looking up its sequence in FIG. 11, as an example of the conventional address transfer method.
In FIG. 11, the terminal A in the address space A is given a private IP address “10.1.1.1” in that address space A, and on the other hand the terminal B in the address space B is given a global IP address “13.1.1.1” in that address space B.
There are registered to NAT some global IP addresses. One of these addresses is “13.1.1.10” for example. Private IP address of address space A should be transferred by the NAT device to this or other global address (See FIG. 11, T1).
On this condition, as terminal A sends a packet which has IP address “13.1.1.1” toward terminal B (FIG. 11,T2), NAT compiles an IP address transfer table which relates IP address “10.1.1.1” of the packet sender to IP address “13.1.1.10” for transfer assigned in the address space B as mentioned above (T3). After this, NAT translates IP address “10.1.1.1” of the packet sender to “13.1.1.10” and sends the packet toward IP address “13.1.1.1” (T4,T5).
Terminal B receives the packet and processes the data in the packet for the sender. When reply packets are demanded by the sender, the terminal B sends packets in reply toward the address “13.1.1.10” of the sender contained in the received packet. Such packets in reply reaches NAT. And NAT refers to IP address transfer table compiled by the manner mentioned above, so as to translate IP address “13.1.1.10” to IP address “10.1.1.1” of the destination (T7). After this, NAT sends the packet to the address space A(that is to say the network given the address space A) (T8).
However, NAT or NAPT only changes IP address of the OSI's third layer. That is to say, NAT or NAPT does not transfer addresses existing beyond the third layer of the multi-media communication protocol for example H323 or SIP (Session Initiation Protocol). So, it was impossible to have telephone communications between the terminals each of which was existing in the different address space.
And, NAT or NAPT needs manual initial registration before translating addresses (See FIG. 11,T1). So, there was also another subject that the operations to use these devices were complicated.